THE NUTRIENTS AND DIGESTION 321 



Digestibility of Feeds. — ^The mere chemical composition of 

 a feedstuff is of little value in poultry feeding unless it is 

 known how much of each nutrient is digestible and avail- 

 able for the fowls. It is not enough, for instance, to know 

 that oats contain 11.8 per cent, protein, 59.7 per cent, carbo- 

 hydrates and 5 per cent. fat. In order to have an intelli- 

 gent basis for feeding, it must also be known what proportions 

 of these nutrients are digestible for poultry and capable of 

 assimilation. 



Ash is usually absorbed by the intestine without change 

 in composition, and cannot be said to undergo digestion in 

 the ordinary sense of the term. Insoluble ash compounds 

 may be rendered soluble by the hydrochloric acid of the 

 glandular stomach, but this can hardly be classed as digestion. 



No nutrient is completely digested and assimilated by 

 any fowl under any condition. The undigested portion 

 passes through the body without change, and has manurial 

 value only. That percentage of a nutrient which is digested 

 is called the digestive coefficient of that nutrient. The 

 digestive coefficients vary for each nutrient and are deter- 

 mined by direct experiment. 



These experiments, which are usually referred to as 

 digestion trials, are made as follows: A fowl is fed a given 

 amount of food, the exact composition of which has been 

 determinediby analysis. All the jntestinal voidings produced 

 during the period are carefully collected, weighed, and 

 ^analyzed. The undigested portions of the nutrients appear 

 in the voidings, and the difference between the amount fed 

 and that excreted, reduced to a percentage basis, represents 

 the digestion coefficient. 



Digestion trials are very much more difficult with poultry 

 than with other farm animals, owing to the fact that the 

 urine is not temporarily stored in the bladder and eliminated 

 through a separate genito-urinary opening, as in mammals, 

 but is conveyed directly from the kidneys through the ureters 

 to the cloaca, where it is constantly mixed with the fecal 

 matter from the intestines. "The fact that the urine arid 

 feces are excreted together has formed the chief obstacle to 

 progress in the performance of digestion experiments with. 

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